Ubuntu Linux Will Work To Slowly Demphasize 32-bit
Canonical isn't yet prepared to drop 32-bit Ubuntu ISOs outright, but over time -- and particularly at or just after Ubuntu 16.04 -- they will work to demphasize the existence of the 32-bit releases and work to push more users to 64-bit Ubuntu as a main focus.
Discussed today during the second day of the online Ubuntu Summit was about when the 32-bit images should stop being made... to which there isn't yet a firm agreement. The 32-bit Ubuntu packages will likely be maintained past whenever the 32-bit images stop being spun, but this probably won't happen until after Ubuntu 16.04 -- the next Long Term Support release in 2016. This session today was a follow-on to the recent discussion about Ubuntu 16.04 potentially being the last 32-bit release.
In the near term, Ubuntu stakeholders will work to encourage more 64-bit Linux adoption, consider shipping a 64-bit Linux kernel for those installing 32-bit Ubuntu on a x86_64 capable system, investigate 32-bit UEFI issues, etc. Long story short is there's likely another two years of 32-bit Ubuntu Linux ISO releases but at least they're working to push 64-bit Linux adoption hardware. It was just last year that 64-bit Ubuntu became the recommended default.
For those interested last month I did some Ubuntu 14.10 32-bit vs. 64-bit benchmarks. You can find more of the Ubuntu developer discussion around the 32-bit Ubuntu abandonment via the session notes and video.